1. Field of the Invention
The invention relates generally to the field of Optics and Electro-optics, and more particularly to stereoscopic image analysis for the purpose of mapping. Still more particularly, it relates to optical and electronic systems for the automation of the stereocompilation process as applied to photogrammetric data reduction.
2. Description of the Prior Art
Electronic scanners and correlation by digital computers have been successfully employed for the automation of the stereocompilation process to perform automatic image-image matching of a stereopair of phototransparencies. Such equipment is elaborate and expensive for the function to be performed.
An alternate approach is the use of optical correlation via the spatial frequency domain for a part of the stereocompilation process. A system for performing this correlation function optically was described by Krulikoski et al. in a number of reports including "Automatic Optical Profiling," Photogrammetic Engineering 37 (No. 1 ), 76-84 (January 1971). Their system is described by the authors as a substantial step toward increasing the speed of an automatic stereocompilation process. Coherent optical multi-channel correlation techniques using Fourier transform holograms as spatial frequency filters were applied to the measurement of x-parallax in stereo photography. The output of their apparatus was produced as an "instant profile" in a correlation plane and displayed an entire x-parallax profile rather than parallaxes point-by-point sequentially. For any sampled y-directed strip of constant x in one of the stereotransparencies, the correlator output provided a simultaneous display of x-parallaxes as a function of the y-coordinate. All of the overlapping imagery was processed by sequentially moving a sampling slit aperture across the stereotransparency.
The further processing of the "instant profile" involved the digitizing of the profile-data, i.e. of x-parallax and corresponding x-y positions for all points of interest, digital computation of corresponding elevations, storage of the elevations of a large number of neighboring points, and then the interpolation between these elevations to draw a contour line at a specified elevation.